Published German patent document DE 43 18 107 describes a sensor for detecting gases flowing in a gas duct, in which the housing that accommodates the sensor element is designed as a tubular metal housing having a longitudinal bore. The outer periphery of the metal housing has a single-piece peripheral flange, which is used for securing the metal housing on a sealing seat formed on the gas duct. A central section of the sensor element is inserted centrally into the metal housing and is secured via a sealing system which presses against both the sensor element and the bore wall of the longitudinal bore, an end section on the measuring gas side and an end section on the connection side of the sensor element projecting from the housing on both sides of the housing. A connecting plug which connects the sensor element to connecting cables is mounted on the connection side end section. The end section on the connection side having connecting plugs is covered by a protective sleeve which is pushed over the metal housing and welded thereto. The end section of the sensor element on the measuring gas side is surrounded by a protective tube having gas passage openings, the housing side end of the protective tube carrying an annular flange pointing outward which is fastened inside the metal housing.
In another sensor for determining the oxygen level in exhaust gases of internal combustion engines, which sensor is described in published German patent document DE 197 39 435, the sensor element is installed in a tubular metal housing on which a sealing flange is formed by first upsetting the tubular element, forming a rounded bulge, and subsequently machining the bulge by swaging in such a way that two sealing surfaces, inclined with respect to one another and axially surrounding the housing, are formed. The sensor element is secured in the housing via a sealing system having a ceramic molded part on the measuring gas side, a ceramic molded part on the connection side, and a sealing element therebetween, and gas-tightly sealed in such a way that the end section of the sensor element on the measuring gas side projects out from the housing. The ceramic molded parts are made of aluminum oxide (Al2O3) and have central bushings for the sensor element. The sealing element made of steatite, which also has a bushing for the sensor element, is inserted, in a pre-pressed state, between the ceramic molded parts. Subsequently, pressure is applied on the ceramic molded part on the measuring gas side using a punch to crush the pre-pressed sealing element and press it onto the housing wall and the sensor element. Subsequently the inside of the housing is shaped to hold the pressure position with respect to the sealing element. The ceramic molded part on the connection side is supported by a radial shoulder inside the housing. A double protective tube having gas passage openings is reverse drawn over the end section on the measuring gas side, its end being pushed into the housing and welded thereto. In the installed position, the sealing flange of the housing rests on a sealing seat formed in a connecting piece of the exhaust pipe and is secured using a cap screw whose annular surface rests on the sealing flange and which is screwed onto an external thread of the connecting piece. The connecting piece gas-tightly surrounds an insertion hole, situated in the measuring gas duct, i.e., the exhaust pipe, for the double protective tube.